A stabilizer is a ball joint part connecting an arm or a strut of a suspension apparatus and a stabilizer apparatus. FIG. 1 is a perspective view showing a schematic structure of a front side wheel of a vehicle. Each suspension apparatus 1 is provided at left and right tires 4 and has an arm 11 and a cylinder 12. A lower end portion of the arm 11 is fixed at a bearing supporting a shaft of the tire 4. The cylinder 12 is elastically movable relatively to the arm 11. A bracket 13, to which a stabilizer link 3 is mounted, is provided at the arm 11. The suspension apparatus 1 supports the weight of a vehicle body that is applied to the tire 4. A stabilizer apparatus 2 is equipped with a bar 21 that is approximately U-shaped, and the stabilizer apparatus 2 is mounted to the vehicle body via bushes 22. The stabilizer apparatus 2 secures rolling stiffness of the vehicle.
The stabilizer links 3 are provided at the bracket 13 of the suspension apparatus 1 and at the end portion of the bar 21 of the stabilizer apparatus 2. The stabilizer links 3 are connected to each other by a support bar 70. The stabilizer link 3 transmits a load, which is generated when the suspension apparatus 1 receives an input from a road surface, to the stabilizer apparatus 2.
FIG. 2 is a side sectional diagram showing a portion of a structure of a specific example of the stabilizer link 3. The stabilizer link 3 is equipped with a ball stud 30, a ball seat 40, a housing 50, and a dust cover 60.
The ball stud 30 has a stud portion 31 and a ball portion 32 which are integrally formed. The stud portion 31 has a tapered portion 33, a straight portion 34, and a screw portion 35. The tapered portion 33 is formed at an upper end portion of the ball portion 32. A collar portion 36 and a projection portion 37 are formed at an upper end portion and a lower end portion of the straight portion 34. An upper end fixing portion 61 of the dust cover 60 abuts between the collar portion 36 and the projection portion 37 at the straight portion 34 so as to be fixed therebetween. The screw portion 35 of the stabilizer link 3 proximate to the suspension apparatus 1 is fixed at the bracket 13 of the arm 11 by screw fastening, and the screw portion 35 of the stabilizer link 3 proximate to the stabilizer apparatus 2 is fixed at the bar 21 by screw fastening.
The ball seat 40 and the housing 50 form a pivot support member that universally supports the ball stud 30. The ball portion 32 of the ball stud 30 is press-fitted into the ball seat 40. The housing 50 holds the ball seat 40 therein. A lower end fixing portion 62 of the dust cover 60 is held between flange portions 41 and 51 of the ball seat 40 and the housing 50. Thermal caulking portions 42 are formed at a bottom portion of the ball seat 40. Each thermal caulking portion 42 projects through a hole 52 of a bottom portion of the housing 50, and a leading end portion of the thermal caulking portion 42 engages with a lower surface portion of the housing 50 (for example, Patent Document 1).
As a material of the housing 50 and the support bar 70, iron can be used. The housing 50 and the support bar 70 are molded in a different shape, respectively, and the support bar 70 is connected to the housing 50 by welding such as resistance welding, etc.
In recent years, in order to reduce the weights of stabilizer links, resin is used as a material for the support bar, and the support bar is formed by an injection molding. In the resin used for the injection molding, a reinforcing fiber such as a fine grass fiber, etc., is usually included.
In a stabilizer link 5 shown in FIG. 3, for example, a housing 80 and a support bar 90 made of resin are integrally molded. The support bar 90 has a top wing plate 91, a bottom wing plate 92, a center supporting plate 93, and ribs 94A and 94B, as shown in FIG. 3A. The wing plates 91 and 92 and the center supporting plate 93 are portions for ensuring longitudinal strength of the support bar 90, and two stabilizer links 5 are connected by extending them in a longitudinal direction. The top wing plate 91 and the bottom wing plate 92 are arranged at an upper end portion and a lower end portion of the center supporting plate 93, and horizontally protrude from the center supporting plate 93 as show in FIG. 3B. In this way, the top wing plate 91, the bottom wing plate 92 and the center supporting plate 93 are arranged, so that a cross section perpendicular to a longitudinal direction has an I shape.
The ribs 94A and 94B are formed between the wing plates 91 and 92, and are portions for ensuring perpendicular strength. The rib 94A is arranged at a longitudinal center portion of the center supporting plate 93, and the ribs 94B and 94B are arranged at a fixed interval from the rib 94A to a longitudinal direction. The ribs 94A and 94B protrude in a horizontal direction to the center supporting plate 93, as well as the wing plates 91 and 92. Here, in the stabilizer link 5, bottoms of a ball sheet and a housing is fixed by an ultrasonic wave caulking. In FIG. 3, the same reference numerals denote the same components as those in the stabilizer link 5 shown in FIG. 2.
The housing 80 and the support bar 90 are formed by injection molding using forming dies with cavities having corresponding shapes thereto. The cavities have a housing forming portion for forming the housing 80 and a support bar forming portion for forming the support bar 90. The support bar forming portion has a wing plate forming portion for forming the wing plates 91 and 92, a center supporting plate forming portion for forming the center supporting plate 93, and a rib forming portion for forming the ribs of 94A and 94B. In this case, a gate for injecting the resin in the cavity is located at a longitudinal and horizontal center portion of the bottom wing plate formatting portion.
In such injection molding, the broader the passage width, the larger the fluidity of the resin. In the support bar 90 of the stabilizer link 5, a plate thickness t1 of the wing plates 91 and 92 (a passage width of the wing plate forming portion) is 4.2 mm, a plate thickness t2 of the center supporting plate 93 (a passage width of the center supporting plate forming portion) is 3.2 mm, and a plate thickness t3 of the rips 94A and 94B (a passage width of the rib forming portion) is 2.2 mm. As described above, the passage widths are set to narrow in an order of the wing plate forming portion, the center plate forming portion, and the rib forming portion. Therefore, the resin in the support bar forming portion flows in an order of the wing plate forming portion, the center plate forming portion, and the rib forming portion, and it is filled in the rib forming portion after filling in the wing plate forming portion and the center plate forming portion.
Patent Document 1 is Japanese Unexamined Patent Application Publication No. Hei 6-117429.
When a longitudinal direction of the reinforcing fiber included in the resin agrees with a direction of strength required in the plates, the strength due to the reinforcing fiber can be sufficiently obtained. In the case of the wing plates 91 and 92 and the center supporting plate 93 having a function which prevents buckling of the support bar 90, the required strength direction is a longitudinal direction of the support bar, and in case of the ribs 94A and 94B having a function which prevents falling of the wing plates 91 and 92, the required strength direction is a perpendicular direction.
The strength of each portion of the support bar 90 is theoretically obtained based on a cross sectional moment, etc. However, it was proven that there was a problem in that the following failure in manufacturing occurs in the ribs 94A and 94B by researching the ribs 94A and 94B of the support bar 90 having the above structure.
When a passage width of a rib forming portion of the forming die is too narrow, flow of the resin from the bottom wing plate forming portion at a gate side to the rib forming portion is decreased by increasing a pipeline resistance in the passage, and as a result, flow of the resin from the top wing plate forming portion of at an opposite side to the gate side is increased. Therefore, since the resin from the top wing plate forming portion and the resin from the bottom wing plate forming portion are joined in a height direction center portion of the rib forming portion or the vicinity thereof, there is a problem in that defects such as weld flow, etc., occur at this junction of the resins. In this case, when turbulent flow is generated by collision, etc., at the junction of the resin, the reinforcing fiber is caught in the turbulent flow, and each reinforcing fiber is arranged in a random direction. Since it is difficult to arrange the reinforcing fiber in the required strength direction as described above, there is a problem in that strength required on the ribs 94A and 94B cannot be ensured. In particular, a perpendicular center portion of the ribs 94A and 94B is a portion in which the generation stress is the maximum, and therefore, the above problem is serious.
In addition, when the passage width of the rib forming portion in the forming die is too wide, minute voids are generated on the ribs 94A and 94B, and there is a problem in that the strength required on the ribs 94A and 94B cannot be ensured. Furthermore, it is preferable that the resin is flowed from the wing plate forming portion to the rib forming portion in the injection molding, since the required strength direction of the ribs 94A and 94B is perpendicular. However, since the resin flows in the support bar forming portion, in an order of the wing plate forming portion, the center supporting plate forming portion and the rib forming portion, and it also flows from the center supporting plate forming portion, and as a result, there is a problem in that the strength required on the ribs 94A and 94B cannot be ensured.
As described above, in particular, in the ribs 94A and 94B, there is a problem in that the required strength cannot be ensured.
Therefore, an object of the present invention is to provide a stabilizer link and a manufacturing method therefor which can ensure strength required in wing plates and a center supporting plate and in a support bar, and which can ensure strength required in ribs.